Method and instrumentation for posterior interbody fusion

ABSTRACT

A method and instrumentation for spinal interbody fusion is disclosed. The instruments and methods are particularly adapted for interbody fusion from a posterior approach to the spine. One instrument is a retractor having a lockable pivotally mounted handle. Another instrument is a template for straddling the dura. A modular distractor is also provided and preferably includes a tapered shaft with a visualization window disposed therein. Yet another instrument is a depth gauge to verify bone opening depth and dimension, preferably including a radiopaque portion. A method contemplates the use of these instruments to prepare a disc space to receive an implant.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/081,206, filed Apr. 9, 1998.

BACKGROUND OF THE INVENTION

The present invention relates generally to surgical procedures forspinal stabilization and more specifically to instrumentation andtechniques for inserting a spinal implant within the intervertebral discspace between adjacent vertebra. More particularly, while aspects of thepresent invention may have other applications, the invention providesinstruments and techniques especially suited for interbody fusion from agenerally posterior approach to the spine.

Various surgical methods have been devised for the implantation offusion devices into the disc space. Both anterior and posterior surgicalapproaches have been used for interbody fusions. In 1956, Ralph Clowarddeveloped a method and instrumentation for anterior spinal interbodyfusion of the cervical spine. Cloward surgically removed the discmaterial and placed a tubular drill guide with a large foot plate andprongs over an alignment rod and then embedded the prongs into adjacentvertebrae. The drill guide served to maintain the alignment of thevertebrae and facilitated the reaming out of bone material adjacent thedisc space. The reaming process created a bore to accommodate a bonedowel implant. The drill guide was thereafter removed following thereaming process to allow for the passage of the bone dowel which had anouter diameter significantly larger than the reamed bore and the innerdiameter of the drill guide. The removal of the drill guide left thedowel insertion phase completely unprotected. Thus, Cloward's method andinstrumentation was designed for and limited to an anterior surgicalapproach and was inappropriate for a posterior application.

Furthermore, B. R. Wilterberger described in a paper entitled “DowelIntervertebral Fusion as Used in Lumbar Disc Surgery” (published in TheJournal of Bone and Joint Surgery, volume 39A, pgs. 234-92, 1957), theunprotected drilling of a hole from a posterior approach into the lumbarspine between the nerve roots and across the disc space, and theninserting a bone dowel into that disc space. While Wilterberger hadtaken the Cloward concept of circular drilling followed by dowel fusionand applied it to the lumbar spine from a posterior approach, he had notfurther improved the method, nor had he advanced the instrumentation toprovide adequate protection for the sensitive vessels and neurologicalstructures adjacent to the operating field.

U.S. Pat. No. 5,484,437 to Michelson discloses a technique andassociated instrumentation for inserting a fusion device from aposterior surgical approach that provides greater protection for thesurrounding tissues and neurological structures during the procedure. Asdescribed in more detail in the '437 patent, the surgical techniqueinvolves the use of a distractor having a penetrating portion that urgesthe vertebral bodies apart to facilitate the introduction of thenecessary surgical instrumentation. The '437 patent also discloses ahollow sleeve having teeth at one end that are driven into the vertebraeadjacent the disc space created by the distractor. These teeth engagethe vertebra to maintain the disc space height during subsequent stepsof the procedure following removal of the distractor. In accordance withone aspect of the '437 patent, a drill is passed through the hollowsleeve to remove portions of the disc material and vertebral bone toproduce a prepared bore for insertion of the fusion device. The drill isthen removed from the sleeve and the fusion device is positioned withinthe disc space using an insertion tool.

While the more recent techniques and instrumentation represent anadvance over earlier surgical procedures for the preparation of the discspace and insertion of the fusion device, the need for improvement stillremains. The present invention is directed to this need and providesconvenient methods and instruments to insure safe and effectivepreparation of a disc space in conjunction with implant placement.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved retractorassembly permitting variable placement of the handle with respect to aretractor blade. The retractor comprises a retractor blade, a shafthaving a first portion connected to the retractor blade, and an oppositesecond portion pivotally connected to a handle. Preferably, the assemblyfurther includes a locking mechanism selectively locking the handle tothe second portion to limit pivotal movement of the handle in relationto the shaft.

In another aspect of the present invention, a method of dura retractionis provided for posterior access to the spine. The method comprisesproviding a retractor having a retractor blade pivotally connected to ahandle, and the handle having a locking mechanism to selectively lockthe handle to the retractor. A portion of the dura is exposed and theretractor is inserted with the handle in an insertion position and thelocking mechanism in a locked position. The dura is then retracted toexpose underlying spinal elements. Preferably, the locking mechanism isunlocked to allow the handle to pivot in relation to the retractorblade. In this aspect, the handle is pivoted to a holding position andlocked to maintain the handle in the locked position.

Yet a further aspect of the present invention is a template forstraddling the dura in a spinal surgery to facilitate marking a surgicalsite to gain access to the disc space in preparation for implantplacement. The template comprises a body having an upper surface and alower surface facing the dura, and an opening formed between the uppersurface and the lower surface. A shaft having a first end and a secondend is connected to the body and extends away from the upper surface.Preferably, a working tube is connected to the body in substantialalignment with the opening and extends from the lower surface, the tubehaving a first diameter. A locator extension engages the body and isspaced from the tube to provide a space for passage of the duratherebetween. The locator extension extends from the lower surface andhas a second diameter that is less than the tube diameter. Optionally,the body may be formed to match the maximum area of the insertioninstrumentation at the engagement with the vertebral bodies, therebyallowing marking of the bone needing removal.

Still a further object of the present invention is to provide a spinaldisc space distractor assembly. Preferably, the distractor includes atapered shaft portion. Optionally, a window may be formed through theshaft for visualization. In one form of the invention, the assemblycomprises a driving portion removably coupled to a distractor tip. Thedriving portion is coupled to transmit rotational and longitudinalforces. Preferably the assembly includes an outer shaft having a firstdriving shoulder for transmitting rotational force end and an oppositesecond driving shoulder for receiving a rotational force. An inner shaftis slidably disposed within at least a portion of the outer shaft, theinner shaft having a first connection end and an opposite secondconnection end. The first connection end is disposed adjacent the firstdriving shoulder. The assembly further includes a distraction tip, thetip having a driving surface adapted for engagement with the firstdriving shoulder and a connection surface adapted for engagement withthe first connection end. A handle interconnects the inner and outershafts and maintains the tip in contact with the outer shaft. In oneembodiment the outer shaft is tapered to provide greater visualization.Further, the outer shaft may have a visualization window extending therethrough.

It is yet a further object to provide an instrument for determining thedepth and size of an opening formed between two adjacent vertebralbodies. The instrument comprises an elongated shaft and preferably aradiolucent tip attached to the shaft, the tip including at least onradiopaque marker. Preferably, the instrument includes a distal tipsized to match the diameter or shape of the opening intending to becreated.

The present invention also contemplates a method of preparing a discspace and inserting an implant. The method utilizes one or more of theinstruments described above to prepare the disc space for receiving animplant.

Related objects and advantages of the present invention will be apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a perspective view of a retractor according to the presentinvention.

FIG. 1(b) is a partial cross-sectional side view of the retractor ofFIG. 1.

FIG. 2(a) is an end view of a shaft of a portion of the retractor ofFIG. 1.

FIG. 2(b) is a side view of the retractor shaft of FIG. 1.

FIG. 3(a) is a side view of the handle of FIG. 1.

FIG. 3(b) is a bottom view of the handle of FIG. 3(a).

FIG. 4(a) is a perspective view of an intraoperative template accordingto another aspect of the present invention.

FIG. 4(b) is a partial cross-sectional side view of the intraoperativetemplate of FIG. 4(a).

FIG. 5 is a perspective view of a further embodiment of anintraoperative template according to the present invention.

FIG. 6 is a perspective view of still a further embodiment of anintraoperative template according to the present invention.

FIG. 7 is perspective view of the intraoperative template of FIG. 6 withhandle and trephine.

FIG. 8 is a perspective view of yet a further embodiment of anintraoperative template according to the present invention.

FIG. 9 is a perspective view of still a further intraoperative template.

FIG. 10 is a cross-sectional view of the embodiment of FIG. 4(a).

FIG. 11 is a perspective view of a distractor according to the presentinvention.

FIG. 12(a) is an exploded perspective view of a modular distractoraccording to the present invention.

FIG. 12(b) is a substantially assembled perspective view of the modulardistractor of FIG. 12(a).

FIG. 13 is a plan elevation of a fully assembled distractor of FIG.12(b).

FIGS. 14(a) through 14(c) are partial cross-sectional side views takenalong line 14 a-14 a showing the modular distractor according to FIG.13.

FIG. 15 is a side elevational view of an outer sleeve according to thepresent invention.

FIG. 16 is a side view of the outer sleeve of FIG. 15 rotated 90° aboutthe longitudinal axis.

FIG. 17 is a perspective view of the outer sleeve of FIG. 15 incombination with the distractor of FIG. 13.

FIG. 18 is a perspective view of a depth stop according to one aspect ofthe present invention.

FIG. 19(a) is a side-elevational view of the depth stop of FIG. 22.

FIG. 19(b) is a side view of the depth stop of FIG. 19(a) rotated 90°about its longitudinal axis.

FIG. 19(c) is a cross-sectional view of the depth stop of FIG. 19(b).

FIG. 20 is a side-elevational view of an alternative embodiment of adepth stop according to the present invention.

FIG. 21 is a perspective view of an outer sleeve in combination with adepth stop and reamer.

FIG. 22 is a perspective view of a depth gauge according to one aspectof the present invention.

FIG. 23 is a perspective view of the depth gauge of FIG. 22 incombination with an outer sleeve.

FIG. 24 is a perspective view of a tap in combination with an outersleeve.

FIG. 25 is a perspective view of an implant inserter in accordance withanother aspect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated devices, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The present invention relates generally to instruments and methods forperforming vertebral interbody fusion. While it should be understoodthat the instruments disclosed herein may have many uses, it isparticularly contemplated that they may be used to perform vertebralinterbody fusion from a generally posterior approach to the spine. Suchprocedures typically involve the placement of dowels or other implantsinto the intervertebral disc space to promote fusion between adjacentvertebral bodies and to stabilization of the spine. Such implants may beformed of metal, ceramics, composites, bone or other bio-compatiblematerials, depending on the properties desired from the implant.

Referring now to FIG. 1(a), there is shown a retractor mechanismaccording to one aspect of the present invention. Retractor 10 includesa handle 12 pivotally connected to a shaft 14 having a distal end 17connected to a retractor blade 16. While retractor blade 16 is shown asa semi-circular blade, it is contemplated that any of a variety ofretractor blade shapes may be utilized in conjunction with handle 12 andshaft 14 of the present invention. Handle 12 is pivotable in relation toshaft 14 and may be releasably connected to shaft 14 adjacent enlargedend 18. As shown more clearly in FIG. 2, enlarged end 18 includes aseries of grooves 24 on its upper surface 36. Handle 12 includes alocking mechanism 22 adapted to selectively engage annular groove 26extending around enlarged end 18 of shaft 14, and at least one ofgrooves 24 disposed on the upper surface 36.

Referring specifically to FIG. 1(b), locking mechanism 22 includes aflange 28 adapted for engaging a portion of annular groove 26 disposedon shaft 14. As shown in FIG. 3(b), flange 28 extends in a semi-circularfashion and includes substantially parallel straight extensions 31 and33 positioned adjacent opening 35. Flange 28 defines an opening 35 forreceiving a portion of the enlarged head 18 of shaft 14 to hold theshaft and handle in mating engagement. Locking mechanism 22 furtherincludes an upper plate 34 having a downwardly extending internalprojection 30 adapted to engage one of grooves 24 on shaft 14. Althoughonly a single projection 30 is shown, it will be understood thatmultiple projections may be provided to engage one or more grooves onshaft 14. Disposed within handle 12 is an inner shaft 23 slidable withinouter shaft 32 to at least partially close opening 35 to prevent passageof enlarged end 18 from the channel formed by flange 28. The position ofinner shaft 23 is controlled by movement of thumb lever 20 slidingwithin slot 21 formed in outer shaft 32. Inner shaft 23 includes aprojection 29 adapted to engage a portion of annular groove 26.Preferably, inner shaft 23 is biased to an extended position shown inFIG. 1(b) by spring 38 captured within outer shaft 32. In the extendedposition, inner shaft 23 retains handle 12 and shaft 14 in lockedengagement.

In a locked position, flange 28 of locking mechanism 22 engages asemi-circular portion of annular groove 26 and projection 29 on innershaft 23 also engages a further portion of annular groove 26. Thisengagement maintains handle 12 and shaft 14 securely engaged. To inhibitpivotal movement in the locked position, grooves 24 on enlarged end 18are urged into engagement with projection 30 of locking mechanism 22,thereby positioning the projection in one of the grooves 24 to preventrotation of handle 12 about the longitudinal axis of shaft 14. In anadjustment position, projection 29 may be partially withdrawn fromannular groove 26 by movement of thumb lever 20 in the direction ofarrow 25. With projection 29 in the adjustment position, there may besufficient transverse movement of shaft 14 within opening 35 todisengage projection 30 from grooves 24 thereby permitting pivotalmovement of handle 12 in relation to shaft 14 without complete removalof the handle. In the adjustment position, inner shaft 23 preventsmovement of shaft 14 entirely out of opening 35, thus maintaining theconnection between handle 12 and shaft 14. With the locking mechanism inthe adjustment position, the handle may be pivotally repositioned to avariety of positions. It will be understood that in a preferredembodiment, shaft 14 includes eight grooves 24, thereby permittinghandle 12 to be locked in eight separate pivotal positions about shaft14. Although eight grooves 24 are shown, it is contemplated that more orless grooves may be provided to accommodate various positions. Moreover,while grooves are shown on the top of shaft 14, it is contemplated thatthese may be placed around the exterior of enlarged head 18 to engage aprojection correspondingly disposed in locking mechanism 22. Further,the placement of grooves and projections may be reversed such that theshaft includes one or more projections mating with grooves in thelocking mechanism. Other mechanisms known to those skilled in the artfor allowing selective pivotal movement between the shaft and handle arecontemplated and come within the scope of the present invention.

In an unlocked position, projection 29 of inner shaft 23 is completelywithdrawn from opening 35 by further movement of thumb lever 20 in thedirection of arrow 25, thereby allowing enlarged end 18 to be removedfrom locking mechanism 22. The locking mechanism may also be placed inthe unlocked position to insert a tool shaft.

Utilization of the above-described retractor device provides severaladvantages over retractors utilizing a fixed handle position.Specifically, in a first locked handle position, a surgeon may positionthe retractor device 10 to most effectively retract a desired neuralstructure or vessel. Once the surgeon has properly positioned theretractor adjacent the desired tissue and the tissue is retracted,handle locking mechanism 22 may be moved to the adjustment position andhandle 12 pivoted about shaft 14 to a position for an assistant tomaintain the tissue or vessel in the retracted position. Often, theassistant will be located on the opposite side of the patient from thesurgeon and it is desirable that the handle be rotated out of thesurgical field to provide the best access and visualization of thesurgical site for the surgeon. Once properly positioned, the lockingmechanism may be returned to the locked position to securely hold thehandle and shaft in the selected arrangement. Further, handle 12 may beremoved from shaft 14 and utilized with a variety of instruments, suchas those disclosed further herein. Use of a removable handle having theadvantages described above may limit the total number of handlesrequired for a surgical procedure or that must be supplied with asurgical set.

Referring now to FIGS. 4(a) and (b), there is shown an intraoperativetemplate 40 according to another aspect of the present invention.Template 40 includes a shaft 42 interconnected with handle 44. Shaft 42is centrally connected to the upper side of template body 48. Templatebody 48 defines a number of bone marking notches 50 around its perimeterand includes an integrally formed guide tube 46 extending from its lowersurface. Although an integrally formed guide tube is shown in apreferred embodiment, it will be understood that a removable guide tubemay be connected adjacent an aperture in the body. Guide tube 46 definesa channel 47 to receive an instrument. Body 50 further defines anopening 49 adapted to receive a locator extension 51.

In FIG. 4(b) there is shown a partial cross-sectional view of thetemplate of FIG. 4(a). Inserted within opening 49 is a removable locatorextension 51 having a head 53. In a preferred embodiment locatorextension 51 may be threadably received with opening 49 to preventdislodgment. Diameter 41 of guide tube 46 is substantially larger thandiameter 43 of locator extension 51. The additional space created byutilization of a locator extension rather than a second guide tube sizedto receive a cutting instrument limits the amount of compression thatthe dura 45 must undergo and increases the possibility that such atemplate may be utilized. Preferably, guide tube 46 and locatorextension 51 are in substantially parallel alignment.

Referring now to FIG. 5, there is disclosed a second embodiment of anintraoperative template according to the present invention. A secondtemplate 52 includes a handle 54 connected to a shaft 56 which iscentrally connected to template body 58. Template body 58 furtherincludes guide tube 60 and integrally formed post 62. A trephine 64 isillustrated extending into and through guide tube 60 with trephinecutting head 66 extending beyond distal end 61 of guide tube 60. Theaddition of post 62 to the template permits a surgeon to straddle thedura and place post 62 to further assist in the alignment of any furthertrephining procedures.

Referring now to FIG. 10, template body 48 includes six indentations 50along the perimeter of the device. The perimeter of the device matchesthe amount of exposure required for placement of a pair of implants.Preferably, the body is sized to match the space needed to place twocylindrical bone dowels. Therefore, if in placing template body 48, bonystructures are encountered which extend into the area needed for implantplacement, notches 68, 70, 72, and similar notches on the other portionof the template permit marking of the interfering structure andultimately passage of a working channel for placement of interbodyfusion devices.

FIGS. 6 and 7 illustrate still a further embodiment of an intraoperativetemplate according to the present invention. Intraoperative template 80includes a shaft 82 and an enlarged end 84 similar to the enlarged end18 previously described on shaft 14 of the retractor mechanism disclosedin FIG. 1. As such, handle 98 is identical to handle 12 and may bepivotally positioned on shaft 82. Intraoperative template 80 includes atemplate body 86, a guiding tube 88, and an aperture 94 extendingthrough template body 86. As shown in FIG. 6, a removable post 92 withattached handle 90 has been placed in opening 94 to drop into a firsttrephine hole or to penetrate the disc annulus to stabilize the templateduring trephining of a first hole through guide tube 88. It will beunderstood that post 92 and handle 90 may be removed for unilateraltemplating if desired.

Referring now to FIG. 7, there is shown the intraoperative template ofFIG. 6 with interconnected handle 98 joined by connection mechanism 100as previously described with respect to the retractor mechanism ofFIG. 1. A trephine 96 is further disclosed extending through guide tube88.

In FIG. 8 there is illustrated a further embodiment of a templateaccording to the present invention. Template 116 has a template body andguide tube as previously described with respect to FIG. 6. In thisembodiment, shaft 117 includes an offset portion 118 laterallyoffsetting enlarged head 119 from the lower portion of the shaft. Itwill be understood that this limits the amount of instrumentation withinthe surgical field and permits greater access.

Referring now to FIG. 9, there is shown yet a further embodiment of anintraoperative template according to another aspect of the presentinvention. Intraoperative template 101 includes a connection mechanism104 on shaft 102, a template body 106, guiding tube 108, and a post 110.In contrast to the previous embodiments, post 110 includes asubstantially straight portion 112 in substantial alignment with theconnection 113 of post 110 to template body 106. Between straightsection 112 and connection 113, is a laterally extending curved portion114. It will be understood that the curvature of rod 112 away from tube108 provides still further space for disposing the dura 116 between tube108 and post 110 during the templating procedure. Post 110 may beremovably secured to body 106. Moreover, post 110 is illustrated havinga particular curve, it being understood that the locator extension maytake an alternative configuration and remain within the scope of thepresent invention.

Referring now to FIG. 11, there is shown a distractor according toanother aspect of the present invention. Distractor 130 includes a shaft131 with a Hudson-type connection 132 and markings 134 indicating thedistraction height created in the disc space by the distraction tip 136.Disposed adjacent indicators 134 is a substantially uniform diameterguiding portion 144. Extending further towards distraction tip 136 is acontinuously tapering portion 142. Disposed adjacent distractor tip 136is a further set of indicators 138, again indicating the height ofdistraction in the disc space created by the orientation of tip 136.Disposed within tapering section 142 is a visualization window 140extending entirely through shaft 131 permitting visualization ofstructures and vessels on the opposite side of the shaft. The distractortip of FIG. 11 is a two-position distractor having an insertion positionwith a first working distraction height. If the first workingdistraction height is insufficient or a greater distraction is desired,the shaft may be rotated 90° to a second greater working distractionheight.

Referring to FIGS. 12 through 14, there is disclosed a modulardistraction assembly 150 permitting interchangeability of distractiontips, as well as the ability to leave the distraction tip disposedwithin the disc space while removing the insertion tool. Referring morespecifically to FIG. 12(a), the modular distraction assembly 150includes a T-handle 180 with a conventional Hudson-type connectionmechanism 181 disposed therein. The assembly further includes an innershaft 152 having an enlarged end 154 adapted for engagement with Hudsonmechanism 181 and an opposite threaded end 156. Inner shaft 152 may bedisposed within outer tube 160. Outer tube 160 includes a slot driver162 and an opposite end driving extension 164 having flats 166 forengagement with the T-handle 180 to transmit rotational force to outertube 160. Preferably, outer tube includes a visualization window 168extending therethrough. Distractor tip 176 has an internal channel 179defining internal threads 177 for engagement with threaded end 156 ofinner shaft 152 and a slot 178 for engagement with the slot driver ofouter tube 160 (see FIG. 14(c)).

Referring now to FIGS. 14(a) through (c), there is shown a cross-sectionof the assembled modular distraction assembly 150. As shown in FIG.14(b), enlarged end 155 of inner shaft 152 is advanced past balls 186such that the balls are adjacent a smaller outer diameter 157 of theinner shaft 152. Collar 184 is then advanced towards outer tube 160 suchthat inclined surfaces 188 extend below balls 186 and reduced internaldiameter portion 190 is disposed adjacent balls 186 to forcibly urgeballs 186 against reduced outer diameter 157 of shaft 152. It will beunderstood that the engagement of balls with inner shaft 152 securelyholds the inner shaft in position. Handle 180 includes a shaft portion181 having a configuration adapted to engage the driving flats ofextension 164. It will be understood that with collar 184 substantiallyadvanced towards shoulder 165, the inner shaft and outer tube aresubstantially engaged with handle 180. To complete the engagement in apreferred embodiment, inner shaft 152 must be threadedly engaged withdistraction tip 176 prior to attachment of T-handle such that the distalend 171 of outer tube 160 engages the enlarged head 173 of distractiontip 176 to secure the outer tube 160 in engagement with handle 180. Itwill be understood that to disengage the assembly, collar 184 must bepulled toward handle 180 until balls 186 are adjacent inclined surfaces188 and allowed to move away from inner shaft 152. In this position,handle 180 may be displaced longitudinally away from outer tube 160 andremoved. Once handle 180 has been removed, inner shaft 152 may berotated to threadedly disengage from distractor tip 176, therebyallowing the inner shaft and outer tube 160 to be disengaged fromdistractor tip 176. Inner shaft 152 is preferably retained within outertube 160 by threads 161. Threads 161 are larger than the internaldiameter of threaded opening 163. For complete removal, threads 161 maybe threadedly passed through threaded opening 163.

Referring now to FIG. 15 and 16, there is shown an outer sleeve inaccordance with another aspect of the present invention. Outer sleeve210 includes a distractor portion 212 having a tip 216 and taperingportion 214 extending back to an area of grooves 218 adapted to engageadjacent bony structures. An opposing distractor portion 213 issimilarly formed. The bone engaging portion further includes spikes 220and 221 adapted to be driven into bony structures adjacent the discspace. Outer sleeve 210 further includes visualization windows 222 and224. Window 222 extends to extended side wall 226. In contrast, window224 extends closer to the engagement end and terminates adjacent sidewall 228. It can be seen that side wall 226 is substantially longer thanside wall 228 along longitudinal axis 211. As shown in FIG. 15, thelonger portion of side wall 226 is provided to engage and protect nerveroots exiting the spinal cord adjacent the surgical site. In contrast,shortened wall 28 provides greater visualization through window 224.Additionally, outer tube 210 includes a markings visualization window232 for visualizing markings on instruments in the tube indicating thedepth of instrument penetration into the disc space.

Referring now to FIG. 17, there is shown a combination of the distractorassembly 150 having a distractor tip 176 in combination with outersleeve 210. Window 224 permits visualization of the distractor assemblywhile window 232 permits visualization of markings along the distractorassembly shaft indicating the depth of penetration of the distractorand/or outer sleeve. It will be understood that in a typical procedure,distraction assembly 150 is placed prior to the insertion and placementof outer sleeve 210.

Referring now to FIGS. 18 through 20, there is disclosed a depth stopmechanism preferably cooperable with the shaft of a tool and an outersleeve as disclosed herein. Such tools can include, without limitation,the reamer and the tap. Depth stop 300 includes an enlargedcircumferential abutment shoulder 310 adapted to engage the proximal endof an outer working sleeve to prevent further advancement of the stopand any interconnected shaft. Stop 300 further includes viewing windows308 to permit visualization of depth markings on a shaft extendingwithin the stop. Stop 300 includes a manually operated collar 302 whichmay be axially displaced along axis 301 in the direction of arrow 305 toallow flexing of fingers 306. Collar 302 is normally urged into anextended position by spring 316. Referring specifically to FIG. 19(c),fingers 306 include projections 304 extending internally. The internalprojections 304 are configured for engagement within grooves definedalong a tool shaft of a working tool. Additionally, each finger includesan external taper portion 312 adapted for engagement with bearingsurface 314 of collar 302. It will be understood that with collar 302 ina retracted position, bearing surface 314 of collar 302 will besubstantially disengaged from taper 312 and thereby permits fingers 306to disengage from the groove of a tool shaft. With collar 302 in theextended position shown in FIG. 19(c), bearing surfaces 314 bear againstthe tapered surface 312 of each finger to urge projections 304 into agroove of a tool shaft. In this manner, a user may quickly and easilydisengage the locking mechanism of the stop to advance or retract a toolshaft and then reengage the stop at the desired position. However,engagement with the tool shaft is indexed by the spacing of grooves onthe shaft so the exact location of the stop may be easily known. Thetool shaft may be rotated with respect to the stop mechanism to displaythe appropriate depth numeral indicated on the shaft in window 308.Preferably, collar 302 will extend at least partially beyond fingers 306to limit the possibility that surgical staff may snag protective apparelon exposed fingers 306.

In a first embodiment shown in FIG. 19(a), collar 302 is retained onhousing 306 by retaining pin 322 extending into the housing and througha slot 320. Retaining pin 322 prevents rotation of collar 232 withrespect to housing 318. In an alternate embodiment shown in FIGS. 24,collar 302 defines an L-shaped slot 324 which permits axial displacementof collar 302 with respect to body 318, as well as a slight amount ofrotation within the slot. It will be understood that the L-shaped slot324 permits the depth stop mechanism to be locked in a disengagedposition which permits free movement of a tool shaft through the depthstop. This is a desirable construction in some instances for easyremoval of the depth stop from the tool shaft, as well as forutilization of the tool without the constraints of a depth stopmechanism.

Referring now to FIG. 21, there is shown an outer sleeve 210 incombination with a depth stop 300 and reamer 351. The reamer 351 isinterconnected with a T-handle 180 having Hudson connection engaged withthe reamer shaft. It will be understood that depth stop 300 has beenpositioned to engage the upper portion of outer sleeve 210 to preventfurther advancement of the reamer beyond the set depth.

Referring now to FIG. 22, there is shown a depth gauge according to afurther aspect of the present invention. Depth gauge 360 includes anupper portion 362 having a plurality of markings 366 indicating thedepth of the distal portion of the gauge into the vertebral bodies.Lower portion 364 is sized to substantially match the outer diameter ofa cylindrical dowel to be inserted into an opening formed betweenadjacent vertebra. It will be understood that close matching of theouter diameter of depth gauge 360 with the desired diameter of the dowelto be placed, will insure that the opening formed between the vertebralbodies in the disc space is substantially clear of debris and closelymatches the outer diameter of the dowel to be placed. Previously, therehas been a possibility that debris could block a portion of the openingdespite the fact that a depth gauge of a smaller diameter may reach thefarthest reaches of the opening. In such a situation, advancement of adowel, particularly in the case of a more brittle bone dowel, may beimpeded by the debris left in the opening, resulting in the possibilityof damage to the dowel and/or the opening when excessive force isapplied to advance the dowel. In a further aspect of the presentinvention, portion 364 is radiolucent and includes a number of markersto identify the location of the depth gauge by radiographic means.Radiomarker 372 indicates the most distal position of the depth gaugeand subsequent position of the implant. Radiographic markings 370 and376 indicate the proximal ends of various sizes of implants. Thedistance 378 between 372 and 370 is approximately 20 mm, a conventionalimplant size, while the distance between 372 and line 376 isapproximately 26 mm, a further conventional implant length.

Referring now to FIG. 23, there is shown the depth gauge of FIG. 22inserted into and extending beyond outer sleeve 210. The depth ofextension beyond outer sleeve 210 of depth gauge 360 is shown by thenumeral in window 232 in the outer sleeve.

FIG. 24 illustrates a tap 390 interconnected with the shaft and handle180 extending through outer sleeve 210. It will be understood thatmarkings on the shaft of the tap may be displayed in window 232 toindicate the length of extension beyond the outer tube. Additionally,the assembly includes an adjustable depth stop 300 which engages theproximal portion of outer sleeve 210 to prevent over-advancement of taphead 390 into the disc space.

Referring now to FIG. 25, there is shown an implant insertion device 400according to the present invention. The implant insertion deviceincludes depth markings along the shaft of the device. Depth markings406 indicate when the dowel is first engaged in the disc space. In thepast, it was possible that when one relied only upon feel, the dowelcould engage obstructions within the working channel of the outer sleeveor other type of inserting device, giving the false impression that theimplant 402 was engaging the disc space and potentially leading todamage to the implant as it was forced against the obstruction. With themarkings 406, multiple markings for different implant lengths, the usercan visually verify whether the implant has engaged the disc space.Markings 404 are provided to indicate the depth the implant has beeninserted into the disc space.

In use, an initial incision provides the approach and exposure of theposterior spinal surgical site. Exposure of the dura is accomplished ina customary fashion. In one aspect of the method according to thepresent invention, a retractor according to the present invention isused to retract the dura. Once retracted, the pivotal handle of theretractor is pivoted out of the way to permit an assistant to hold theretractor without interfering in the operating field.

A template in accordance with the present invention may then be placedto extend on both sides of the dura simultaneously with a guide tubepositioned on one side and a locator extension positioned on theopposite side. A trephine is then passed through the guide tube and intothe disc space to remove a portion of the disc and adjacent tissue. Thetemplate may be removed and repositioned to again straddle the dura withthe locator extension in the previously trephined hole and the guidepositioned on the opposite side of the dura. Again, the trephine ispassed through the guide tube and into the disc space to form an openingtherein. With the template remaining in position across the dura, thesurrounding bone structures are evaluated for removal to permitplacement of a guide sleeve. If bone elements, facet or lamina, arepositioned beneath the template body, a marking device such as acautherizer is used to mark the offending structure in one of thenotches provided. After the bone structures have been marked, thetemplate is removed and the bone removed in a conventional manner.Preferably, the template is repositioned to straddle the dura and thefield is again checked to verify that a guide tube may be placed withoutobstruction. If not, further bone marking and removal is conducted. Oncethe space is prepared for guide tube placement, the template is removed.

In accordance with another aspect of the invention, a distractor isinserted into the disc space in one of the previously trephine openings.In a similar manner, a second distractor is inserted into the secondtrephined opening. If necessary, a distractor having two working heightsis inserted in a first smaller height and rotated 90 degrees afterinsertion to a second larger height. Moreover, a tip having the desiredconfiguration may be selected and mounted on the modular distractionassembly 150 prior to insertion. In some instances, the tip may bedisconnected from the distractor assembly and temporarily left in thedisc space.

The further description of the method will be described with respect toplacement of single dowel, it being understood that the steps may berepeated on the opposite side to implant a second implant. A guide tubeis positioned over the distractor and advanced until the distractingflanges are positioned in the disc space. It will be understood that theenlarged portion on the distractor shaft guides the guide tube into aconcentric position about the distractor. Once the guide tube issecurely seated, the distractor may be withdrawn. The disc space willthen be prepared to receive an implant having a preselected length anddiameter. A reamer of the appropriate diameter is selected and a depthstop according to the present invention is positioned on the shaft atthe preselected depth markings. The reamer is rotatably advanced intothe disc space until the depth stop engages the guide tube to limitfurther advancement. Preferably, a depth gauge according to the presentinvention is inserted to verify complete reaming to the preselecteddepth and removal of debris. If a threaded implant will be used, a depthstop will be positioned on a tap shaft at the preselected depth. The tapis rotatably inserted into the disc space until the depth stop engagesthe guide tube. The tap is removed and the depth gauge may be reinsertedto verify that the proper sized opening has been formed and issubstantially unobstructed. At this point an implant is inserted usingthe implant inserter. Once the implant is inserted, the guide tube maybe withdrawn and the procedure repeated on the opposite side.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A template for straddling the dura in a spinalsurgery to facilitate marking a surgical site, said template comprising:a body portion having an upper surface and a lower surface, and anopening formed between said upper surface and said lower surface; ashaft having a first end and a second end, said first end connected tosaid upper surface; a working tube positioned in substantial alignmentwith said opening and extending from said lower surface, said tubehaving a first diameter; and a locator extension engaged with said body,said locator extension extending from said lower surface and spaced fromsaid working tube to provide a space for the dura, said locatorextension have a second diameter that is less than said first diameter.2. The template of claim 1, wherein said locator extension is removablyengaged with said body.
 3. The template of claim 1, wherein said body issized to approximate a maximum area of an instrument set, and said bodyincludes a perimeter with a plurality of notches for marking tissue thatmust be removed to accommodate the instrument set.
 4. The template ofclaim 1, further including a handle pivotally connected to said secondend and a locking mechanism controllable to selectively limit pivotalmovement between said shaft and said handle.
 5. The template of claim 1,wherein said locator extension is solid.
 6. The template of claim 1,wherein said working tube is integral with said body.
 7. The template ofclaim 1, wherein said locator extension includes a connection endconnected to said body, an opposite engagement end and a curved portionbetween said connection end and said engagement end.
 8. The template ofclaim 1, wherein said shaft includes an offset segment between saidfirst end and said second end.
 9. The template of claim 3, wherein saidbody includes two inter-connected semi-circular lobes defining themaximum area of an instrument set.